Technical and economic factors continue to drive the evolution of semiconductor processing equipment. The semiconductor industry demands fabrication machines with a capability to process semiconductor wafers at high speed with substantial uniformity and reliability. Integrated circuit fabrication commonly involves numerous process steps with fabrication machinery processing semiconductor wafers at high speed to create structural features with high precision. Measurements are commonly made between process steps to verify features are within tolerances demanding a capability to perform non-destructive inspection and analysis of semiconductor wafers.
Optical metrology is a highly useful technique for non-destructive analysis. Examples of optical metrology include ellipsometry, reflectometry, scatterometry, and others. Ellipsometry involves analysis of changes in polarization state of probe illumination. Reflectometry relates to analysis of changes in illumination intensity. Scatterometry is analysis of diffraction in response to illumination that creates optical scattering of a probe beam. As semiconductor geometries constantly evolve to smaller integrated circuit critical dimensions, optical interrogation wavelengths decrease.
Because the semiconductor fabrication process takes place in a strictly controlled environment, the impact of non-destructive analysis equipment and techniques on the environment is desired to be minimal. Accordingly, desired characteristics of analysis equipment include aspects such as small size, capability to remain conveniently located with respect to process chambers and equipment, capability to perform measurements and analysis without contacting the semiconductor wafers, and capability of remote control.
Measurements are commonly made between process steps. A measurement technique that delays the process awaiting measurement result confirmation between process steps is inherently inefficient. Minimal impact on fabrication throughput is sought. Non-destructive analysis equipment and techniques can improve throughput by reducing or eliminating delay for analysis equipment placement, and reducing time for measurement acquisition and analysis.